The invention relates to an electro-mechanical switch which is opened or closed when exposed to a magnetic field. More specifically, the invention relates to a liquid level float switch in which the water level of a container determines the position of a magnet and the location of the magnet determines whether the magnetically actuated switch is opened or closed.
A float switch is an electro-mechanical device which allows for an electrical switch to be opened or closed depending on the fluid level in a container. The float switch allows for automatic operation of devices depending on the level of fluid, such as the operation of pumps, or the opening or closing of valves.
Float switches are common in industry and in the prior art. Most float switches contain an electrical switch imbedded within the body of the float switch device. The electrical switch is actuated upon physical movement of the portion of the float switch device containing the electrical switch or upon physical movement of another portion of the float switch device. Many prior art float switches contain a mechanical actuator. For example, a mechanical switch may be embedded within a stem. The float may be fixably attached to a container wall or structure within a container in such manner that the float hangs upside down when the water level within the container is low. When the water level within the container rises, the float is raised into an upright position with respect to its fixed location within the container, and the mechanical connection within the float opens or closes an electrical switch.
Another common type of water level switch is a magnetically actuated switch imbedded into an elongated tube. The elongated tube has a buoyant float moveably surrounding the tube with a metallic or magnetic component such that the float may move up or down along the length of the tube as the water level within a container rises or lowers. When the metallic or magnetic component of the float is raised or lowered to correspond with the position of the magnetic switch within the elongated tube, the switch within the tube is magnetically actuated and the electrical circuit is opened or closed.
Liquid level switches are often used as safety devices within liquid containing tanks or vessels. For instance, it is important to maintain a proper water level within a heating vessel such that heating elements do not overheat when there is an inadequate supply of water or other fluid to the tank or in the event that there is a leak in the tank. In such a situation it is important that a safety sensor or switch be available to disconnect the heating elements in the event of a fluid heating situation or discontinue liquid flow to a container in a leaking vessel situation.
Applicant is aware of the following U.S. Patents concerning electro-mechanical liquid level switches/sensors.
Struzik et al., U.S. Pat. No. 6,253,610, teaches a wiper for use in a system for monitoring fluid level in a container. The wiper is equipped with a body portion, a first and second lengthwise end, a first and second side, and a pair of contact members electrically connected to one another.
Robinson, U.S. Pat. No. 6,195,013, teaches a float sensor having a mounting bracket which incorporates an O-ring seal and mounting fingers which locks the mounting bracket to a tank flange. A reed switch housing is welded to the end of the tube opposite the mounting bracket.
Issachar, U.S. Pat. No. 6,218,949, teaches a liquid level apparatus which generates an alarm signal, discontinuing an operation such as heating, when the liquid in a controlled vessel has reached a predetermined level. The operation of the apparatus may be based on various physical properties, such as magnetic, acoustic or electrical properties.
The prior art liquid level switches have the disadvantage of not having means of indicating whether the switch had been previously operated or not. This is often the case in a slow leaking vessel which, because of its slow leaking, cycles between a high liquid level and a low liquid level status. In such a case the leaking of the vessel would not be immediately obvious to one only intermittently observing the status of the circuit controlled by the liquid level switch. Similarly, liquid level switches of the prior art would allow repeated connection and disconnection of heating elements or other devices in the event of a cycling liquid level. Additional sensors may be added to the prior art liquid level switches to indicate the previous operational history of the switches, however, these added components detract from the reliability of the switches, especially in harsh working environments.
The principal object of this invention is to provide a liquid level float switch that must be manually reset once activated.
Another object of this invention is to provide a liquid level float switch which stays in the activated position after initial activation regardless of future changes in liquid level within a container.
The invention is a float-switch that automatically actuates a switch continuously on sensing a change in a liquid above a threshold level, where said float-switch requires manual reset once the switch has been actuated. Manual reset is effected by moving the float-switch below the threshold level.
The invention is comprised of an elongated cylindrical stem having linear positions comprising: a lower sectional length with a lower stop, a non-actuation sectional length, a switch actuation sectional length, and an upper sectional length with an upper stop. A magnetically actuated switch, preferably a reed switch, along with its associated electrical connectors, is embedded in the stem, at a position adjacent to the upper stop. The magnetically actuated switch is located at the switch actuation sectional length, and the electrical connectors preferably extend through the stem exiting the upper sectional length.
A fixed magnet, immobilized by a fastening means to the stem, forms the upper stop of the stem, just above the magnetically actuated switch. A retaining clip, affixed to the stem, forms the lower stop. The retaining clip is most preferably a push nut. A float that is preferably cylindrical is mounted upon the stem between the fixed magnet and the retaining clip. The float has an annular wall defining a center hole through which the stem protrudes.
The float is free to move up and down the stem, and in a vertical orientation, the float responds to a liquid having a density greater than the overall density of the float. The float always seeks to move toward the surface of the liquid. The range of movement is confined to the length of stem defined on one end by the retainer clip, and on the other end by the permanent magnet.
The float contains a magnetic portion, where the magnetic portion is preferably a toroidal magnet with a core that is oriented to be magnetically attracted to the fixed magnet, where the stem moves through the core of the toroidal magnet. The toroidal magnet has a magnetic field at the core, wherein the magnetic field is sufficient to actuate the magnetic actuated switch. The magnetic portion is arranged in or on the float such that an upper face on the magnetic portion corresponds in shape to a lower face on the fixed magnet. When the float moves up the stem in response to a change in the liquid level, once it reaches the threshold level, which corresponds to the very near proximity of fixed magnet, the float is magnetically drawn to the fixed magnet. The force of attraction is sufficient to support the weight of the float, and the upper face of the magnetic portion is abutted to the lower face of the fixed magnet. The position of the float is fixed by the mutual magnetic attraction between the fixed magnet and the magnet portion of the float. The position of the float, abutting the fixed magnet, aligns the magnetic actuated switch in the core of the toroidal magnet, therein maintaining continuous actuation of the switch.
The switch can be de-actuated by manually moving the float down the stem toward the retainer clip, in the region of the stem displaced from the switch, which was previously identified as the non-actuation sectional length. While the float remains in this region of the stem the magnetic switch is not actuated. It therefore follows that so long as the level of liquid is below the threshold level of liquid, the magnetic switch will not be actuated.
In most magnetically actuated switches, and especially with regard to a reed switch, the nominal position when the switch is not actuated is where the contacts of the switch are open. A typical reed switch, sometimes called a reed relay, has ferromagnetic arms that, in the absence of a magnetic field, are parallel and not touching. In the presence of a magnetic field, the arms or reeds are brought into contact.